The invention relates to an assembly for the parallel processing of data streams by means of satellite communication links, which consists of a first subassembly for a data transmission operation and/or of a second subassembly for a test operation.
The invention also relates to a method for the parallel processing of data streams by means of satellite communication links, wherein the method is operated with a first operating mode for a data transmission operation in which useful data in the form of a data stream are transmitted via a number of carriers, and/or a second operating mode for a test operation in which test data are transmitted via a number of carriers.
When processing data streams by means of satellite communication, the following requirements essentially occur:                Efficient performance of so-called In Orbit Tests (IOTs) with particular focus on measuring accuracy, measurement time and little influencing of existing communication links        Increasing the data rate per communication link in the case of uniform occupancy of the frequency spectrum        Increasing the data rate per transponder/channel/satellite (data throughput), improving the degree of utilization (so-called fill rate), i.e. as uniform and complete utilization as possible of available transponder bandwidth and transponder power        Overcoming capacity limitation due to analog interferers and overcoming data rate restrictions due to regulatory limitations of the transmitting power (frequency and orbit coordinates)        
In the text which follows, the individual requirements listed above will be discussed.
In Orbit Tests (IOTs):
So-called In Orbit Tests (IOTs) are performed at regular intervals for protecting warranty claims, for checking the contractually agreed performance parameters or for testing components in the space segment, but also for measuring the transmission quality. In this context, the satellite components to be surveyed are removed from useful operation, as a rule, and surveyed with the aid of special test signals and measuring methods from the ground. Apart from the costs for the measurements which, as a rule, is a service of third parties, this mainly results in losses of turnover since no fees can be charged for rented satellite capacity for the duration of the measurements.
At the same time, such IOTs have a high contractual relevance since the satellite manufacturer must always guarantee product quality over the entire product life cycle to his customer, typically the satellite service provider. The service provider then derives from this a certain availability of the satellite link and a quality of service which, in turn, it guarantees to the end user, as part of service level agreements (SLAs).
IOTs are thus necessary and unavoidable because they serve to establish the bearer of the economic load of unfulfilled SLAB. The quality of an IOT concept is therefore assessed primarily by means of the accuracy of measurement and the necessary measuring time within which no useful data can be transmitted. An ideal and superior concept allows the transmission of useful data for all relevant measurements even during the measuring. Furthermore, such a concept allows the user, i.e. the operator of the communication link to survey the required parameters independently and in the course of operation without collaboration by third parties so that he can verify directly the degree of fulfillment of the SLAB he was assured of.
Data Rate Per Communication Link:
The requirements for higher data rates per communication link are placed more and more into the center of future solutions. A higher data rate allows the transmission of more information within the same time frame and without increasing the exclusively needed frequency spectrum and is thus of great economic interest.
Increasing the Data Rate Per Satellite: (Data Throughput)
A spectrum fragmentation is understood to be a mostly irregular breaking of a frequency spectrum into information-carrying and unused frequency ranges. This spectrum fragmentation represents a great challenge to satellite and teleport operators because unused spectrum in conjunction with existing power reserves of the same transponder is equivalent to gain losses which must be minimized. In this respect, it must be noted in explanation that a satellite operator always attempts to release transponder power and transponder bandwidth in equal proportions of the resources available overall. This corresponds to a uniformly equivalent division of the available power to the transponder bandwidth and allows an again uniform utilization of the transponder in conjunction with further operational advantages, such as lower losses by mutual interference between the communication links. In addition, the method takes into account the fact that often several links of the same type, e.g. several television channels, are transmitted per transponder. In the text which follows, it is thus assumed that unused transponder bandwidth must be equated with an also freely available equivalent rating.
In most cases, transponder spectrum is leased together with the fitting equivalent rating from a teleport operator with a satellite operator in a greater extent and over a relatively long period of time. The teleport operator, in turn, distributes the spectrum in relatively small blocks of variable size which are then leased to the end user.
Due to, for example, differently long contract period, failure of a contractual partner, hiring of further capacities, spectra released in the course of the conversion from analog to digital data transmission (key word: digital dividend) and the like, a fragmented spectrum is rapidly produced. This becomes economically fatal if the sum of the free positions/gaps in the spectrum and the transmitting power of the satellite in principle still provide for communication services but this is not possible due to the fragmentation of the spectrum. In practice, fragmented free bandwidth occurs when several customers with single narrow-band links discontinue these at different times. Apart from the transponder bandwidth, the corresponding equivalent rating naturally also becomes available. A superior method is capable of economically utilizing this free bandwidth and power in parts or all together when the individual blocks for occupancy with new communication links are indeed too small but the sum of the available narrow blocks would still be adequate for the operation. Quotable sources here are the State of the Satellite Industry Report (Satellite Industry Association, June 2010), Satellite Communications & Broadcasting Markets Survey Forecasts to 2019 (Euro Consult 2010), Boeing Commercial Communications Satellites (GEO) Jun. 30, 2010 and How Many Satellites are Enough? A Forecast of Demand for Satellites, 2004-2012 (Futron).
Capacity Limitation By Analog Interferers:
Physical, that is to say technical and production-related interference mechanisms in the analog components lead to the transmitted and received signal, respectively, experiencing a multiplicity of the most varied types of signal distortions, caused, for example, by phase noise, DC component, frequency offset, nonlinearities, jitter and I-Q asymmetry. In principle, such disturbances always arise where analog modules are used. In the case considered here, therefore in the transmitting ground station, in the satellite transponder and in the receiving ground station.                Transmitting ground station: the digital/analog conversion is followed by analog processing stages such as, e.g., mixing with the carrier frequency and signal amplification. In this context, each stage leads unavoidably to a more or less strong linear and/or nonlinear signal distortion. Whilst linear distortions can be eliminated by known methods and thus play a subordinate role, there is still a great demand for avoiding/compensating for nonlinear distortions. The nonlinear distortion is particularly strong in the case of a simultaneous operation of several carriers because in this case, there is additive heterodyning of the signals before the actual disturbance.        Satellite transponder: there are many analog modules in the satellite transponder so that interactions between the individual carriers (adjacent channel interference—ACI) also occur here which magnifies the problem of nonlinear distortion even further.        Receiving ground station: in principle, signal distortions also arise in the receiver chain, i.e. before the signal digitization. In comparison with the other two sources (transmitting ground station and satellite), however, these distortions can be considered to be significantly smaller and can be neglected in most cases.        
Considered in summary, the transmitting ground station and/or the satellite can be considered as main interference sources. The extent of contribution of the two positions is here dependent on the respective utilization of the ground station involved and of the satellite. If, e.g., only one signal is transmitted by a ground station involved, but the satellite transponder occupied is fully utilized, the distortion of the signal from the ground is very low but the induced distortion in the transponder is very high.
Quotable sources here are Abschlussbericht Studie Bundeswehr IT-Amt “Bandbreiteneffiziente Satellitenkommunikation” (Final Report Study IT Office German Federal Armed Forces “Bandwidth-efficient satellite communication”) AUDENS Telecommunications Consulting GmbH, 2008, Final Report Study IT Office German Federal Armed Forces, reference number: E/IB2M/AA048/7F010 “Reduktion intermodulationsbedingter Kapazitätsverluste im Systemverbund SATCOMBw Stufe 2” (Reduction of intermodulation-related capacity losses in the combined system SATCOMBw stage 2) NRADIOS GmbH, 2010, “Satellite Communications Systems”, Gerard Maral, Wiley & Sons, 2009, and “RF Power Amplifiers for Wireless Communications”, Steve C. Cripps, Artech House, 2006.
A further problem is represented by the so-called ASI (adjacent satellite interference). ASI is the signal component received by a satellite B from a ground station although this station does not wish to uplink to this satellite B but to another satellite A, and also conversely (downlink). ASI is a result of inadequate antenna gains (beam focusing of the antennas) and, respectively, inadequate gain decoupling of the antennas from the point of view of the receiver (spatial separation of the signals). ASI leads to it not being possible to arbitrarily increase the transmitting power on the ground and at the satellite output without disturbing third-party satellites or third-party ground stations.
It is easily understandable that both signal distortions can be mapped directly onto the achievable data rate because the associated disturbances reduce the ratio of useful signal power and interference signal power at the respective receiver.
The sections following describe the current state of the art. At the moment, the current performance of IOTs is a very long-winded and time-consuming process. This is mainly due to the fact that the test equipment currently available on the market is not capable of performing effective wide-band tests. Although there would be the possibility of generating wide-band test signals for shortening the measuring time. This, however, conflicts with the measurements having to be performed with high accuracy, that is to say with a high C/N (Carrier to Noise) or SNR (signal-to-noise-ratio). To generate a signal with very wide bandwidth with high C/N, high powers would have to be radiated on the ground over a wide band. But in this respect, limits are prescribed by the regulating authority (e.g. frequency mask). In addition, the desired aim of such measurements at the same time with the useful data traffic in the transponder could obviously not be achieved by this means.
Currently there are two approaches for countering this problem:                High-power, narrow-band carriers        Low-power, wide-band carriersNarrow-Band Carriers:        
In the first, currently typical case, a narrow-band test signal is generated which is then progressively shifted from one test frequency to the next similar to a spectrum analyzer. Naturally, this produces a long test phase which is equivalent to a downtime of the satellite and thus entails the corresponding economic consequences. Apart from the obvious economic disadvantages, contradictory or poorly comparable measurement results can also be increasingly expected with this approach which arise plainly from the change in timing of the transmission channel during the measurements (e.g. weather influences). These results are not wrong but distort the view and do not reproduce the momentary characteristics of the overall system. In addition, enormous efforts are generally made to survey the changes in the transmission channel at the same time with the IOTs and calibrate the IOT measurement results subsequently.
For this purpose, separate technical devices must be kept available which are associated with considerable investment costs. This is extremely uneconomical for the predominant number of operators of teleports and of communication links which is why IOTs are offered today only by a few service providers with great market power.
Wide-Band Carriers:
Apart from the progressive shifting of a test signal, there is also a so-called spread-spectrum approach which spreads a sinusoidal carrier widely with the aid of a sequence and thus pushes it below the (thermal) noise level. In this way, the test signal is nearly invisible in the carrier for existing communication links so that these can also continue to be operated during the measurements. On the ground, a very good C/N is achieved again after the despreading. The advantage of this method is that the transmission of useful data can be continued during the measurement, but this method, too, is not of advantage with respect to the measuring time. It is, therefore, used predominantly for monitoring purposes. In addition, separate technical devices must be kept available also for this measuring method which, today, are also associated with very high investment costs. Feeding the test signal into the existing transmitting and receiving paths of the useful signals is often particularly expensive in this context because, apart from the technical expenditure, additional problems of calibration are added. In order to separate the actual effects of the satellite from possible influences of these ground-based signal paths, further measurements must be performed at the ground stations which will also lead to constructional and technical changes. For many operators, this, too, is uneconomical which is why they prefer the service again.
Since the permissible radiated power is limited by regulation, an approach for increasing the data rate of a communication link according to the prior art, which is well suited to satellite communication, is the parallel operation of a plurality of frequency bands/channels at the same time.
The current ground-based communication technology does not allow any inherent parallel processing of several channels. If it is desired to manage this with the current modem technology, the simultaneous operation of several individual modems is necessary. This means that at the transmitter side, a data stream to be transmitted must be divided into several modems, processed separately and, after analog/digital conversion, combined again synchronously at the output of each modem. At the receiver side, an equivalent inverse operation must be carried out.
Current systems already use a similar simplified method. The user information to be transmitted is divided already at a higher protocol layer (IP level) with the aid of a router or multiplexer into several subchannels and then supplied to various standard single-channel modems. Particularly advanced systems integrate these signal-channel modems in the same housing so that the impression of “one modem” is produced for the customer although the signal streams are not connected to one another. This variant, therefore, does not represent any technological development but can be called a slightly changed marketing strategy. The completely independent signal streams of the various modems are transmitted later via a common high-frequency path and the same antennas to one, several or also different receivers where the inverse operations then take place.
Here, too, it can be easily appreciated that the method described has several disadvantages at once:                Increased total weight of the ground stations (each individual modem contributes to this), problematic especially in mobile or transportable use        Increased power consumption in operation (each modem consumes current and must be cooled additionally), problematic especially in mobile or transportable use        The ground station must always be designed for the worst case, i.e. for the data streams to be transmitted simultaneously at a maximum in the boundary case. This is not the most economic solution since the contribution of the modems to the total price increases linearly with a number of data streams.        Synchronization problems (the functionality of the modems must be matched to one another, high technological expenditure; such a solution on the physical layer, i.e. before/after the DA/AD conversion, has not been known hitherto which is why the distribution of the information at a higher protocol layer (IP level) is being resorted to today)        Increased susceptibility to interference (a discrete implementation is more susceptible to mechanical influences due to its structure)        
With respect to an increase in the data rate per satellite, also called data throughput increase, the following must be taken into consideration. The spectrum fragmentation is inversely proportional to the so-called fill rate which is also called load rate per satellite or utilization rate.
The fill rate quantifies the utilization of a satellite with regard to frequency spectrum and transmitting power and can be 100% at maximum.
If the fragmentation of the spectrum is too great or if the fill rate exceeds a predetermined barrier so that no further services can be supported even though sufficient frequency spectrum and transmitting power is still available overall, replanning of the channel/transponder occupation or also of the satellite occupation takes place. This planning is in most cases performed by a very experienced person and with software support. To aggravate matters, preexisting communication links should not be changed, if possible, since in most cases a fixed frequency and bandwidth has been leased to the end user and/or many satellite terminals, especially in crisis regions or regions with poorly developed infrastructure, operate unmanned today.
If the technical changes discussed have to be performed and this cannot be done remotely, this often involves high costs for the operator of the communication links since, in most cases, he is not on site with his own personnel and thus has to commission subcontractors.
To this is added that the approach of replanning is extremely inflexible because it is only when it is really necessary that such a large incision is made in all existing communication links. However, this also means that ad-hoc or short-term enquiries for more spectrum are associated with high financial expenditure. The operator of the system will often even reject short-term enquiries for new spectrum since the achievable additional income will not cover the costs for replanning all existing connections, also called line-up.
Analog interferers will result in a limitation of capacity in the processing of data streams.
Prior investigations have shown that the spectral efficiency of the satellite link can be increased considerably especially by bandwidth-efficient transmission methods. At the same time, it was found that, caused by nonlinear components, the maximum data rate of various links is limited significantly by intermodulation-related degradations of the signal quality. Higher data rates can thus be implemented only by accepting a reduced power efficiency of the ground station and/or of the space segment. Furthermore, elaborate methods for optimizing the carrier occupancy under intermodulation disturbances must be used, the degrees of freedom in the occupancy and combinations of narrow or weak carriers per transponder being distinctly restricted. In systems having a highly heterogeneous architecture for the types of ground station to be operated at the same time (small and large stations, high-power and low-power stations, stations for single links and multichannel stations etc.), these degrees of freedom are of decisive significance.
The problems of ACI are currently counted in such a manner that the space between the transmitting frequencies per channel is correspondingly increased and, if necessary, the transmitting power is reduced. The latter leads to the analog modules then operating in a linear range. The problem of ASI is significantly influenced by the antenna gain. In this case, geographic or frequency-related decoupling of the coverage areas and limitations of the permitted transmitting power are used. However, both of these lead directly to the bandwidth efficiency/SNR being significantly reduced and thus also the achievable data rate.